TweetFollow Us on Twitter

C++ Methods, Fortran
Volume Number:7
Issue Number:2
Column Tag:Jörg's Folder

Related Info: Quickdraw

C++ Methods In FORTRAN

By Jörg Langowski, Editorial Board

“C++ Methods in FORTRAN”

This article had to come. Next thing you’ll see, you may think, is calling Eiffel from Forth. But seriously, implementing cross-language calling very often helps you to understand how one particular language really works and how to get most out of it. Also, the Fortran run time system has some advantages, like well-designed console I/O that may help in debugging, file I/O, an easily accessible output window, and therefore adding it may be very helpful in some applications. So here we go, and write a C++ method in Language Systems Fortran.

C++ methods are really independent subroutines, and the association between a method and its class is done through the header file - on the source code side - and through the modified method name on the object code side. When you define two different classes with methods of the same name, as in

// 1

class aaa {
 public:
 void doit();
}

class bbbb {
 public:
 void doit();
}

the methods are usually defined in a place different from where they are actually used. In fact, most often they may be pre-compiled in a library. The linker can distinguish between the two different doit methods, because their symbolic name on the linker level is modified by the class name. The two methods’ names in this case would be: doit__3aaaFv and doit__4bbbbFv.

C++ Function Name Encoding

To remind you of the C++ linker naming conventions: the first part of the linker name is the method name (doit), followed by two underscores. Then follows the class name, preceded by the number of characters in that name. Appended to that are some symbols describing the parameter list. In our case, for methods taking no parameters, it is simply “Fv”. F stands for a function, v for a void parameter list. I am not describing all the modifiers that are used in creating a linker name out of a C++ method name; the full encoding scheme is described in the AT&T C++ release notes, chapter 6, page 22.

Usually, you never see the encoded names; only when e.g. a method is defined in a class header file, then referenced by some code using objects from that class, but never actually implemented, the linker might complain about a missing function. There, you will probably have seen those funny names already, and used the MPW unmangle tool to make sense out of them.

Here, we want to go the other direction. When we implement a C++ method in some non-object language, we must write a routine that has the encoded method’s name. The easiest way to find out about the linker name of a C++ method is not to construct it yourself (you never get it right in the first place), but just to define the method in the class header, use it in the code, and never actually implement it. The linker will tell you in its error message what function it is looking for.

That way I found out that the name for the method pascal void FtnCall() in the class TMacTutorDocument is FTNCALL__17TMACTUTORDOCUMENT. The characters “Fv” are not appended here, and the name is written in all capitals, because of the “pascal” keyword. This also means that all external Pascal-type methods of the same name in the same class will have the same linker name, regardless of the argument list.

Language Systems Fortran, of course, uses Pascal calling conventions, so a method written in Fortran will have to be defined in C++ as pascal. We want to pass some parameters, so lets define an argument list:

{2}

pascal void FtnCall(short *menuitem, long k, float *r);

The method will later be called from a menu handler, just for the fun of it, and we pass the number of the menu item selected, and some numbers. Note one restriction here: LS Fortran symbolic names are limited to 31 characters, so don’t use too complicated class and method names if you don’t want to run out of space.

The Sample Program

We use the sample program that I showed you in V6#1: Apple’s C++ mini-application skeleton. You should now go back to your library and get that MacTutor issue, or reorder it, because we obviously cannot reprint its full source here. Listing 2 only shows those parts that have been changed.

In the constructor and destructor methods of the application class we have added calls to InitFortran() and ExitFortran() for initializing the Fortran run time system at the start of the program and leaving it properly at the end. During the program, then, the run time system is at our disposal. The Fortran method is defined in the class TMacTutorDocument. It is used in the TMacTutorApp class, in its DoMenuCommand method:

// 3

x = 4.567;
fMacTutorCurDoc->FtnCall(&menuItem,3456,&x);

This way we have some calls by reference (standard Fortran calling convention), and one call by value.

The Fortran routine (listing 1) receives the three parameters in the same order. Furthermore, on every method call a handle to the method’s current object (this) is pushed on the stack after all the method’s parameters. The Fortran code has to take that extra parameter into account. Thus, the first line of the Fortran routine will be

C 4

subroutine FTNCALL__17TMACTUTORDOCUMENT
 (menuitem,%val(k),r,%val(this))  .

menuitem and r are passed by reference, k is received by value (Language Systems Fortran has an option for receiving parameters by value in the subroutine definition). this is also received by value. Through this, we can access the instance variables of the method’s current object. We also define the list of instance variables, which becomes rather complicated as we have to dereference handles in the (Languages Systems) Fortran way. The structure definitions at the beginning of the Fortran routine show you how to do that.

this points to the beginning of the object’s instance variables, starting with those of the topmost ancestor class and descending through the class hierarchy. In our case, we have a window pointer fDocWindow and the pointer to the virtual methods table vptr from the TDocument class, then the instance variables of TMacTutorDocument, fItemSelected and fDisplayString.

The main body of the routine displays the passed parameters and some information about the instance variables in the Fortran output window.

That’s all! You’re now able to add Fortran code to C++ programs as you like, and have it behave like real C++ methods.

Listing 1: C++ method written in Fortran

CC++ test method written in Language Systems Fortran
CFor editing, some of the lines had to be split. I have not
Ccreated proper Fortran continuation lines, because a. C I’m lazy and 
b. I think the text can be read better that 
Cway -- jl --

 subroutine FTNCALL__17TMACTUTORDOCUMENT
 (menuitem,%val(k),r,%val(this))
Cpascal void FtnCall__17TMacTutorDocument
 (short *menuitem, long k, float *r, 
 struct TMacTutorDocument **);
 include “Quickdraw.f”

 structure /MTDocVars/
 record /WindowPtr/ fDocWindow
 integer*4 vptr
 integer*2 fItemSelected
 record /StringPtr/ fDisplayString
 end structure
 
 structure /MTDocPtr/
 pointer /MTDocVars/ p
 end structure
 
 structure /MTDocHdl/
 pointer /MTDocPtr/ h
 end structure
 
 record /MTDocHdl/ this
 
 integer*2 menuitem

 integer top,left,bottom,right
 
 call MoveOutWindow (20,260,490,340)
 write (*,*) “Arguments to FtnCall:”,menuitem,k,r
 write (*,*) “fItemSelected = “,this.h^.p^.fItemSelected
 write (*,*) “fDisplayString = 
 “,this.h^.p^.fDisplayString.sptr^
 
 top    = this.h^.p^.fdocwindow.wp^.portrect.top
 bottom = this.h^.p^.fdocwindow.wp^.portrect.bottom
 left   = this.h^.p^.fdocwindow.wp^.portrect.left
 right  = this.h^.p^.fdocwindow.wp^.portrect.right
 write (*,*) “doc window = “,top,left,bottom,right
 return
 end
Listing 2: Changes to the .cp and .h files from the V6#1 example

File MacTutorApp.make:

OBJECTS = TApplication.cp.o TDocument.cp.o 
 MacTutorApp.cp.o MacTutorDoc.cp.o 
 MacTutorGrow.cp.o FtnCall.f.o
HEADERS = MacTutorApp.h MacTutorDoc.h 
 MacTutorGrow.h

TApplication.cp.o ƒ TApplication.cp TApplication.h
  CPlus  TApplication.cp
TDocument.cp.o ƒ TDocument.cp TDocument.h
  CPlus  TDocument.cp
MacTutorApp.cp.o ƒ MacTutorApp.make 
 {HEADERS} MacTutorApp.cp
  CPlus  MacTutorApp.cp
MacTutorDoc.cp.o ƒ MacTutorApp.make 
 {HEADERS} MacTutorDoc.cp
  CPlus  MacTutorDoc.cp
MacTutorGrow.cp.o ƒ MacTutorApp.make 
 {HEADERS} MacTutorGrow.cp
  CPlus  MacTutorGrow.cp
FtnCall.f.o ƒ MacTutorApp.make FtnCall.f
  Fortran -mc68020 -mc68881 -opt=3 -bkg=0 FtnCall.f

MacTutorApp ƒƒ MacTutorApp.make {OBJECTS}
 Link -w -t APPL -c JLMT 
 “{CLibraries}”CRuntime.o 
 {OBJECTS} 
 “{Libraries}”Interface.o 
 “{CLibraries}”StdCLib.o 
 “{CLibraries}”CSANELib.o 
 “{CLibraries}”Math.o 
 “{CLibraries}”CInterface.o 
 “{CLibraries}”CPlusLib.o 
 #”{CLibraries}”Complex.o 
 “{FLibraries}FORTRANLib.o” 
 -o MacTutorApp

MacTutorApp ƒƒ MacTutorApp.make MacTutorApp.r
 Rez MacTutorApp.r -append -o MacTutorApp

File MacTutorApp.h:

class TMacTutorApp : public TApplication {
public:
 TMacTutorApp(void); // Our constructor
 ~TMacTutorApp(void);
 // need a destructor to call EXITFORTRAN

private:
 // routines from TApplication we are overriding
 long HeapNeeded(void);
 unsigned long SleepVal(void);
 void AdjustMenus(void);
 void DoMenuCommand
 (short menuID, short menuItem);

 // routines for our own devious purposes
 void DoNew(void);
 void Terminate(void);
};

File MacTutorDoc.h:

class TMacTutorDocument : public TDocument {
  protected:
 short fItemSelected;
 // string corresponding to menu item selected
 StringPtr fDisplayString;

 void DrawWindow(void);

  public:
 TMacTutorDocument(short resID, StringPtr s);
 ~TMacTutorDocument(void); 
 // routine to access private variables
 void SetDisplayString (StringPtr s) {fDisplayString = s;}
 short GetItemSelected(void) {return fItemSelected;}
 void SetItemSelected(short item) {fItemSelected = item;}

 // methods from TDocument we override
 void DoUpdate(void);
 
 // Fortran calling;
 pascal void FtnCall(short *menuitem, long k, float *r);
};

File MacTutorApp.cp:

pascal void initFortran();
pascal void exitFortran();

// Methods for our application class
TMacTutorApp::TMacTutorApp(void)
{
 Handle menuBar;

 initFortran(); // initialize Fortran runtime system
 
 // read menus into menu bar
 menuBar = GetNewMBar(rMenuBar);
 // install menus
 SetMenuBar(menuBar);
 DisposHandle(menuBar);
 // add DA names to Apple menu
 AddResMenu(GetMHandle(mApple), ‘DRVR’);
 DrawMenuBar();

 // create empty mouse region
 fMouseRgn = NewRgn();
 // create a single empty document
 DoNew();
}

TMacTutorApp::~TMacTutorApp(void)
{
 exitFortran(); // exit Fortran runtime system
}

void TMacTutorApp::DoMenuCommand
 (short menuID, short menuItem)
{
 short  itemHit;
 Str255 daName;
 short  daRefNum;
 float  x;// for testing the Fortran call
 WindowPtrwindow;
 TMacTutorDocument* fMacTutorCurDoc =
 (TMacTutorDocument*) fCurDoc;

 window = FrontWindow();
 switch ( menuID ) {
 case mApple:
 switch ( menuItem ) {
 case iAbout:    // About box
 itemHit = Alert(rAboutAlert, nil);
 break;
 default: // DAs etc.
 GetItem(GetMHandle(mApple), menuItem, daName);
 daRefNum = OpenDeskAcc(daName);
 break;
   }
 break;
 case mFile:
 switch ( menuItem ) {
 case iNew:
 DoNew();
 break;
 case iClose:
 if (fMacTutorCurDoc != nil) {
 fDocList->RemoveDoc(fMacTutorCurDoc);
 delete fMacTutorCurDoc;
   }
 else CloseDeskAcc(((WindowPeek) 
 fWhichWindow)->windowKind);
 break;
 case iQuit:
 Terminate();
 break;
   }
 break;
 case mEdit: // SystemEdit for DA editing & MultiFinder 
 if ( !SystemEdit(menuItem-1) ) {
 switch ( menuItem ) {
 case iCut:
 break;
 case iCopy:
 break;
 case iPaste:
 break;
 case iClear:
 break;
    }
   }
 break;
 case myMenu:
 if (fMacTutorCurDoc != nil) {
 switch ( menuItem ) {
 case item1:
 fMacTutorCurDoc->
 SetDisplayString(“\pC++”);
 break;
 case item2:
 fMacTutorCurDoc->
 SetDisplayString(“\pSample”);
 break;
 case item3:
 fMacTutorCurDoc->
 SetDisplayString(“\pApplication”);
 break;
 case item5:
 fMacTutorCurDoc->SetDisplayString(“\pHave Fun”);
 x = 4.567;
 fMacTutorCurDoc->FtnCall(&menuItem,3456,&x);
 break;
    }
 fMacTutorCurDoc->SetItemSelected(menuItem);
 InvalRect(&(window->portRect));
 fMacTutorCurDoc->DoUpdate();
 }
 break;
   }
 HiliteMenu(0);
} // DoMenuCommand


 

Community Search:
MacTech Search:

Software Updates via MacUpdate

Latest Forum Discussions

See All

How to get started with Prisma
If there's one thing people like to do more than taking pictures with their smartphones, it's tinkering with those photos in some way. Numerous apps have sprung up over the last several years that allow you to use filters and special effects to... | Read more »
6 Pokemon GO updates you can expect, acc...
Pokemon GO had a scheduled appearance at this year's San Diego Comic-Con for a while, but it was only relatively close to the show that it was upgraded to a spot in Hall H. That's the biggest venue at SDCC, one usually reserved for the largest... | Read more »
How to evolve Eevee in Pokemon GO
By now, almost everyone should be hip to how to evolve Pokemon in Pokemon GO (and if not, there's a guide for that). Just gather enough candy of the appropriate type, feed them all to the Pokemon, and evolution happens. It's a miracle that would... | Read more »
CSR Racing 2: Guide to all game modes
It might not seem like there are all that many ways to go fast in a straight line, but CSR Racing 2 begs to differ. [Read more] | Read more »
Bulb Boy (Games)
Bulb Boy 1.0 Device: iOS Universal Category: Games Price: $2.99, Version: 1.0 (iTunes) Description: Multi-award winning 2D point & click horror adventure about a boy with a glowing head. | Read more »
5 top free emoji keyboard apps
If we're not at peak emoji yet as a society, it feels like we definitely should be. The emoji concept has gone far beyond what anyone in Japan could have envisioned when the people there unleashed it on an unsuspecting world, but the West has... | Read more »
How to unlock more characters in Disney...
One of the big charms of Disney Emoji Blitz is seeing a wide variety of beloved Disney and Pixar characters transformed into smiling emojis. Even someone like the sneaky Randall from Monsters Inc., who probably never cracked a smile on film, is... | Read more »
Cubway (Games)
Cubway 1.0 Device: iOS Universal Category: Games Price: $1.99, Version: 1.0 (iTunes) Description: Cubway is a journey with an abstract story of lifecycle of rebirth, called Samsara. Guide the cube through the long way full of dangers... | Read more »
Colorcube (Games)
Colorcube 1.0 Device: iOS Universal Category: Games Price: $1.99, Version: 1.0 (iTunes) Description: Turn pieces and blend colours in this minimal yet visually stunning puzzler.Over 200 handcrafted and challenging levels. Features... | Read more »
Doodle God Griddlers (Games)
Doodle God Griddlers 1.0 Device: iOS Universal Category: Games Price: $4.99, Version: 1.0 (iTunes) Description: | Read more »

Price Scanner via MacPrices.net

13-inch 1.6GHz/128GB MacBook Air on sale for...
Amazon has the 13″ 1.6GHz/128GB MacBook Air on sale for $200 off MSRP for a limited time. Shipping is free: - 13″ 1.6GHz/128GB MacBook Air (sku MMGF2LL/A): $799.99 $200 off MSRP Their price is the... Read more
13-inch 1.6GHz/256GB MacBook Air on sale for...
Amazon has the 13″ 1.6GHz/256GB MacBook Air on sale for $200 off MSRP for a limited time. Shipping is free: - 13″ 1.6GHz/256GB MacBook Air (sku MMGG2LL/A): $999.99 $200 off MSRP Their price is the... Read more
Free iOS Business App notably* Helps Service...
PayStudio Inc. has introduced their new business app notably* 1.0, developed for iPhone and iPod touch. notably* was specifically developed to help service and trade professionals go digital and... Read more
27-inch iMacs on sale for $200 off MSRP
Amazon has 27″ iMacs on sale for $200 off MSRP including free shipping: - 27″ 3.3GHz iMac 5K: $2099 $200 off MSRP - 27″ 3.2GHz/1TB Fusion iMac 5K: $1799.99 $200 off MSRP - 27″ 3.2GHz/1TB HD iMac 5K... Read more
Mac Pros on sale for $200 off MSRP
B&H Photo has Mac Pros on sale for $200 off MSRP. Shipping is free, and B&H charges sales tax in NY only: - 3.7GHz 4-core Mac Pro: $2799, $200 off MSRP - 3.5GHz 6-core Mac Pro: $3799, $200... Read more
Save up to $600 with Apple refurbished Mac Pr...
Apple has Certified Refurbished Mac Pros available for up to $600 off the cost of new models. An Apple one-year warranty is included with each Mac Pro, and shipping is free. The following... Read more
Apple price trackers, updated continuously
Scan our Apple Price Trackers for the latest information on sales, bundles, and availability on systems from Apple’s authorized internet/catalog resellers. We update the trackers continuously: - 15″... Read more
13-inch 2.5GHz MacBook Pro (Apple refurbished...
Apple has Certified Refurbished 13″ 2.5GHz MacBook Pros available for $829, or $270 off the cost of new models. Apple’s one-year warranty is standard, and shipping is free: - 13″ 2.5GHz MacBook Pros... Read more
21-inch iMacs on sale for up to $120 off MSRP
B&H Photo has 21″ iMacs on sale for up to $120 off MSRP including free shipping plus NY sales tax only: - 21″ 3.1GHz iMac 4K: $1379 $120 off MSRP - 21″ 2.8GHz iMac: $1199.99 $100 off MSRP - 21″ 1... Read more
Charitybuzz Set to Auction Unique Apple-1 Com...
Offering an opportunity to own the computer that sparked a revolution, on Monday, July 25, leading online charity auction platform Charitybuzz will auction what is claimed to be the world’s most... Read more

Jobs Board

*Apple* Retail - Multiple Positions, Willow...
Job Description:SalesSpecialist - Retail Customer Service and SalesTransform Apple Store visitors into loyal Apple customers. When customers enter the store, Read more
*Apple* Evangelist - JAMF Software (United S...
The Apple Evangelist is responsible for building and cultivating strategic relationships with Apple 's small and mid-market business development field teams. This Read more
*Apple* Solutions Consultant - APPLE (United...
Job Summary As an Apple Solutions Consultant, you'll be the link between our future customers and our products. You'll showcase your entrepreneurial spirit as you Read more
*Apple* Professional Learning Specialist - A...
Job Summary The Apple Professional Learning Specialist is a full-time position for one year with Apple in the Phoenix, AZ area. This position requires a high Read more
*Apple* Picker - Apple Hill Orchard (United...
Apple Hill Orchard, Co. Rte. 21,Whitehall, NY 9/7/16-10/228/16. Pick fresh market or processing apples Productivity of 60 boxes and 80 boxes processing fruit per Read more
All contents are Copyright 1984-2011 by Xplain Corporation. All rights reserved. Theme designed by Icreon.